This invention relates to a coil, and, more particularly, to a coil wound on a magnetic core for use in a transformer or a reactor.
Usually, such coils are formed by winding conductors edgewise. The conductor used for such an edgewise-wound coil has a rectangular transverse cross-section and wound on a magnetic core with its longer sides of the rectangular cross-section placed perpendicular to the surface of the core. Thus, edgewise-wound coils can provide a reduced size transformers or reactors. An example of such prior art edgewise-wound coil is shown in FIG. 1.
This coil includes a magnetic core 2 with an insulating layer 4 disposed on an outer surface of the core 2. A conductor 6 is wound on the insulating layer 4. The conductor 6 has a rectangular transverse cross-section and is wound on the core 2 with the longer sides of the rectangular cross-section kept perpendicular to the outer surface of the core 2. A distance d between adjacent conductor turns is small, e.g. 2 mm.
In order to prevent adjacent conductor turns from contacting with each other, an insulating spacer 8 having a comb-shaped cross-section is used, with a spiral groove 8a formed therein fitted over the conductor 6 to hold the respective conductor turns in place. The distance between adjacent groove turns is equal to the distance d between adjacent conductor turns. The width of the groove 8a is equal to the dimension of the short sides of the cross-section of the conductor 6.
Alternatively, a spacer 10 like the one shown in FIG. 2 may be used. The spacer 10 is disposed on the magnetic core 2. A spiral groove 10a is formed in the spacer 10. The groove 10a has a width equal to the dimension of the shorter sides of the cross-section of the conductor 6. The distance between adjacent turns of the groove 10a is equal to the distance between adjacent conductor turns. The conductor 6 is wound in such a manner that respective conductor turns are fitted into respective groove turns, whereby the respective conductor turns are kept spaced from each other.
The width of the groove 8a or 10a of the spacer 8 or 10 of the above-described prior art coil must be equal to the length of the short sides of the cross-section of the conductor 6. Also, the distance between adjacent turns of the groove 8a or 10a must be equal to the distance between adjacent ones of the turns of the conductor 6. In order to further down-size transformers, the distance between adjacent conductor turns may have to be reduced, but it is difficult to manufacture a spacer with a smaller distance between adjacent groove turns. When a spacer with a comb-shaped cross-section is used for a smaller conductor turn spacing winding, teeth between adjacent groove turns may be broken. These problems are hindrance to the down-sizing of transformers. The same problems are encountered not only in down-sizing transformers but also in down-sizing of reactors. In other words, the use of edgewise-wound winding cannot always sufficiently down-size transformers and reactors.
An object of the present invention is to provide a configuration of coils which enables down-sizing of coils by reducing the spacing between adjacent coil conductor turns, while maintaining insulation between conductor turns.
According to the present invention, a coil is provided, which may be used as part of, for example, a transformer or a reactor. The coil includes a magnetic core and a winding disposed on the core. The magnetic core may have one of various shapes, such as a rectangular shape, a U-shape and a ring-shape. The winding is formed by winding a conductor on the magnetic core to form a plurality of conductor turns. The conductor turns are substantially equally spaced from each other on the core. Either coated or naked conductor can be used. An insulating layer may be disposed between the magnetic core and the conductor. The insulating layer may cover the entire outer surface of the core, or it may cover only part of the outer surface of the core. In case a rectangular magnetic core is used, the insulating layer may be formed to cover only the four corner portions.
An insulating member is wound on the magnetic core in a plurality of turns so that the insulating member may be placed in each of the spaces between adjacent conductor turns. Each turn of the insulating member is in contact with the conductor turns on the opposite sides. After being wound on the core, the insulating member may be hardened.
The insulating member may be deformable into a flat shape by the conductor turns with which it contacts. For example, the insulating member may have a circular transverse cross-section with a diameter larger than the spacing between adjacent conductor turns, or it may have a rectangular or square transverse cross-section with a larger dimension in the direction of the spacing of the conductor turns than the conductor turn spacing. In either case, when the insulating member comes into contact with the conductor turns, it is flattened. Accordingly, it eliminates the need for adjusting beforehand the diameter or the dimensions of the insulating member to the spacing between the conductor turns.
The conductor may have a rectangular transverse cross-section with the longer sides placed substantially perpendicular to the outer surface of the magnetic core. In other words, the conductor may be wound edgewise on the core. The edgewise winding of a conductor enables down-sizing of a coil, as described previously. Accordingly, when it is employed in the present invention, further down-sizing can be realized.
The conductor and the insulating member may be wound together around the magnetic core. According to the prior art described with reference to FIG. 1, in which the spacer 8 is used to hold the conductor 6 in place, separate steps are required for winding the conductor 6 around the core and for placing the spacer 8 with respect to the conductor turns, which is a cause for a low working efficiency. In contrast, winding the conductor and insulating member together can increase the working efficiency.